After the Roman era, the two islands are passed to the Byzantine Empire in 200 AD where the population is mostly concentrated in the urban centers of Halkida due to port and so it becomes a transit mall.

Thereafter, Evia passes on to the Franks and the same period was given as fief to the Flemish knight Jacques d 'Avesne. In 1204 starts the Venetian rule of the Franks which now has taken the name "Negroponte". In 1278 Knight Likarios with the help of the Byzantine Emperor Michael VIII Palaeologous, occupies all the castles, in a final decisive battle in 1278, in which he looses from the Venetians and the winner now settled in the Fyllo Castle for a short period. But then again the island passed to the Venetians until 1470 that passed onto the hands of the Ottomans.

The island Skyros after the conquest of Byzantium from the Crusaders in 1204 passed into the hands of the Venetians and the Franks as the conquest by the Ottomans and in 1538, under Turkish- occupied it suffered greatly from pirates.

In June of 1470 in Chalkida, after 17 days of defense, the small garrison and inhabitants headed the last Eneto Bailo Paolo Eritzo falls and is occupied by the Ottomans, with 300 ships and 300,000 troops, led by Mehmet the Conqueror and having followed the largest slaughter that history has witnessed, makes pashalic and calls Egripo ( Evrippos ) .

The period was tough for all of Euboea, especially Chalkida and Karystia, like all conquered parts of Greece. In 1688 the attempts by foreign forces to recapture the city of Chalkida failed. Eventually, Chalkida was liberated in March 25th 1833 and became the capital of the prefecture of Evia.

Skyros had contributed substantially in terms of both money and manpower to the struggle for national independence,. It had sent many sailors to the national fleet, offered shelter to the warlords, elected many members to the pro-independence Society of Friends, and offered shelter to thousands of refugees fleeing from various cities of Greece.

Visitors to both islands will see scattered Castles and Towers, everywhere mainly remnants of the Venetian - Frankish era and some of the Ottoman.

Particularly worth visiting are the following attractions that symbolize this period:

The Karababa fortressin Chalkida was built in 1684 and is regarded as post-Byzantine fortress of Ottoman origin.

The fortress still standing today was built by the Turks in 1684, in order to protect Chalkis by the Venetians. Designed by Venetian Tzerolimo Gallup with a Venetian architecture. The position of the Castle has been identified by some scholars to the ancient city Kanithos as sporadic traces preserved buildings and graves at the soil surface.

The hill was fortified probably for the first time during the Roman period, but it is certain that he had fortified the Byzantine period, during the Venetian and the first centuries of Ottoman rule.

The Castle of Skyrosin Chora was built on top of a rockhill with 3 sides to end in steep cliffs, making it impenetrable to intruders. The castle of Skyros towers above what was once the fortified main town of Chora. While it is not accessible to visitors as it is being renovated due to damage by earthquakes, it is still interesting to learn about this structure and fort around it.

The Tower Avlonariou in the region of Kymi was constructed in the 1st century by Venetians. In 1953 the Venetian tower was preserved and restored and is probably the most beautiful and well preserved medieval tower of Evia. Used by Venetians as the center of a system of optical telegraph and had correspondence with other towers that has survived in poor or mediocre condition. The Windows are located at the middle and upper part of the tower, while the lower portion only brought boxes of small arms and the height is 19 meters. In accordance to tradition, the first municipality town hall of the Distion housed in the Venetian Tower had four floors and the second floor was the City Hall of Avlonariou.

The Royal Tower in Halkida originates Venetian and was built in the 12th century, the formula is: Castle - Towerhouse.

The Twin Towers Lelantine Chalkida built by Venetians in 1205 AD. In the heart of Lilantio field outside Halkida onto a rocky but smooth hill with two peaks, the base of which passes the River Leland, were its built two towers which are preserved in good condition, to control and secure the waters of the river for the best of Halkida and watering the rich plains. Sources say the 1,429 in one of the two towers probably lived the waterward, i.e, a Venetian officer who oversaw the flow of the river, irrigation of crops and maintenance of the marvelous water supply system of Halkida.

It should be said that the towers of Evia, belong to a class of defensive structures, which developed during the 11th century and was widespread in medieval Europe.

The Venetian Castle Fylla in Chalkida built by Venetians in the 13th century. And is called Filla ( Phylla ) Baron Enetokastello the 13th century, the seat of the legendary local Likarios knight who tried and succeeded for a while to give the freedom to the Euboian.

The Castello Rosso (CastelloRosso) in Karysto was built in 1209 -1216 by the Venetians is situated on a hill on Mt. Ochi. Due to the volume and the position that iis built, it dominates the entire region. The position that it has been built has plenty of trees, springs and streams, essential for the survival of the castle in case of siege.

The fort was originally built in 1030 AD by Byzantines, immediately after the capture of the island by the Franks and changed several owners until 1833 when it was delivered to the Greeks. The castle, because of the technical, but also the natural fortifications was impregnable. The castle and the area around it is ideal for naturalist tour.

The Tower Drosinis Gouves- Artemision is built on a hill dominating the area. It is two-storey 100 sqm with stone walls of 1m wide. Venetian architecture is particularly an important property for the region. It was built in the 19th century by its then Turkish owner, Ivraim Aga. After 1821 the property passed into Greek hands and today it belongs to the municipality of Gouves.